1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method for substrate processing of a multilayer film stack. The invention is particularly useful for fabrication of flat panel displays.
2. Description of the Related Art
Fabrication of semiconductor integrated circuits (IC) and flat panel display (FPD) devices require processing of multilayer film stacks to create devices, conductors and insulators on a substrate. One example of a multilayer film stack is a thin film transistor (TFT) structure useful for fabricating liquid crystal display (LCD) devices. FIG. 1 depicts an exemplary bottom gate structure of a thin film transistor 1 having a glass substrate 10 and an optional underlayer 20 formed thereon. A bottom gate formed on the underlayer 20 comprises a gate electrode layer 30 and a gate insulation layer 40. The gate electrode controls the movement of charge carriers in a transistor. The gate insulation layer 40 electrically isolates the gate electrode layer 30 from a bulk semiconductor layer 50 and a doped semiconductor layer formed thereover, each of which may function to provide charge carriers to the transistor. A source region 70a and a drain region 70b formed in the doped semiconductor layer is patterned and isolated by an interlayer dielectric/etch stop layer 60 formed over the bulk semiconductor layer 50. A conductive layer is deposited over the doped semiconductor layer to form a source contact 80a disposed on the source region 70a and a drain contact 80b disposed on the drain region 70b. Finally, a passivation layer 90 encapsulates the thin film transistor 1 to protect the transistor from environmental hazards such as moisture and oxygen. The gate electrode layer 30 generally comprises a conductive metal material. The gate dielectric layer 40, the bulk semiconductor layer 50, and the doped semiconductor layer generally comprises a silicon-containing material.
In general, the substrate for device fabrication is subjected to various processes, such as sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), lithography, etching, ion implantation, ashing, cleaning, heating, annealing, and the like in a specific multi-step fabrication sequence to process layers of metal and silicon containing films thereon. For example, a process chamber is usually configured to perform a single step of the fabrication sequence and the substrate is processed through steps of deposition, patterning, lithography and etching repeated multiple times. A number of process chambers can also be coupled together to a central transfer chamber, having a robot therein to facilitate substrate transfer between the process chambers, to perform one or more substrate processing steps in a single processing platform, such as a cluster tool, examples of which are the families of AKT PECVD, PRODUCER®, CENTURA® and ENDURA® processing platforms available from Applied Materials, Inc., of Santa Clara, Calif.
Typically, the substrate is repeatedly taken in and out among various process chambers and/or cluster tools, partially because a specific substrate processing platform requires a special fabrication sequence. Another reason is that different types of films generally require different types of process chambers and chamber peripherals that may not be technically capable or economical to be coupled together in a single processing system. In addition, in between each step, the surface of the previous thin film may need to be treated, such as annealing to form an interlayer or cleaned by a cleaning solution to remove any surface residues, by-products, contaminants, before taking to the next substrate processing system.
As an example, FIG. 2 depicts a prior art example of a method 200 for processing a film stack having a silicon-containing film and a metal film. The silicon-containing film can be deposited on a substrate in a CVD chamber of a first processing system at step 210. The surface of the substrate is inspected at step 220 and additional patterning, lithography and etching steps may be needed. Since the surface of a silicon-containing film tends to be oxidized when exposed to air so the deposited silicon-containing film needs to be cleaned and/or processed immediately within certain time frame due to the increase potential for particle contamination, moisture penetration, and surface oxidation before and/or after a next patterning step or deposition step. Often times, the next film may contain metal or other materials and may need to be deposited by a different type of process chamber or cluster tool. In this case, the substrate is removed from the vacuum environment of the first substrate processing system and transferred to a hydrofluoric acid cleaning station to clean the surface of the silicon-containing film at step 230. After the deposited silicon-containing film on the surface of the substrate is cleaned, at step 240, the substrate may again need to be immediately transferred, to a second processing system for additional deposition, etching, annealing, and cleaning steps. For example, the substrate after cleaning may need to be additionally processed within 30 minutes to prevent the surface of the silicon-containing film from further oxidation, moisture penetration, and contamination. Then, at step 250, a metal film is deposited over the silicon-containing film on the substrate in a PVD chamber of the second processing system. Thereafter, at step 260, the metal film on the surface of the substrate is inspected again and additional lithography and etching steps are performed. As silicon deposition, metal deposition, and etching processes are typically performed in separate processing systems/tools, the cost for fabricating devices on substrates is high due to the number and size of different tools required and the expense of additional steps or substrate transfer between tools during processing. Moreover, the number of substrate transfer between different tools has an adverse effect on product yields and throughput.
Further, as the demand for semiconductor and flat panel devices continues to grow, there is a trend to reduce cost by increasing the sizes of the semiconductor substrates, glass substrates, and the like for large scale fabrication. For example, glass substrates utilized for flat panel fabrication, such as those utilized to fabricate computer monitors, large screen televisions, displays for PDAs and cell phones and the like, have increased in size from 550 mm×650 mm to 1500 mm×1800 mm in just a few years and are envisioned to exceed four square meters in the near future. Thus, the dimension of a substrate processing system has become ever so large. The cost associated with chamber parts and tool components configured to process large area substrates continues to escalate dramatically. To cut down the cost and reduce surface contamination, it is desirable to design a novel fabrication sequence to eliminate or combine one or more processing steps and to develop processing tools to accommodate sequential processing steps in the same tool for such large area substrates in high throughput and yet in a compact and reduced footprint.
Therefore, there is a need for an improved method and apparatus to process multilayer metal and silicon-containing thin films.